The present invention relates to a turbine rotor blade having a region hardened by heat treatment at a blade tip end as an erosion shield.
In a low pressure stage of a steam turbine, the turbine rotor blade rotates at a high speed in wet steam, and therefore, the turbine rotor blade is subjected to erosion due to collision with water droplets that have condensed from the wet steam. In the regions subjected to erosion, stress concentration increases, and therefore, cracks sometimes occur from those regions.
In recent years, the blade length has tended to be made long in order to increase the output power of turbines and enhance efficiency. As the blade length increases, the circumferential velocity of the blade tip ends increase, and therefore, erosion resistance even higher than before is required.
Thus, as the measures to reduce erosion, there are known the method which bonds a cobalt alloy plate to a blade tip end by electron beam welding or silver blazing, and the measures which harden a blade tip end by heat treatment such as laser heating. In the case of hardening by heat treatment, the hardness distribution in the radial direction has not been especially considered in the prior arts (for example, refer to JP-A-2004-52673 and JP-A-54-77806).